A cleanroom is only as clean as the filter at the end of its air path. Where a standard HEPA stage handles the majority of critical applications, some processes demand removal efficiency measured in the fifth decimal place. A ULPA filter meets that requirement, capturing particles at 99.9995 % and above under EN 1822. This guide covers the efficiency classes, the non-partition construction that keeps operating costs down, and how to specify and maintain these filters in critical environments.
ULPA vs HEPA: Where the Line Falls
The difference between HEPA and ULPA is a matter of efficiency class rather than principle. Both media remove particles mechanically, and both are graded under the same European standard, EN 1822. HEPA filters cover classes H13 and H14; ULPA filters begin at U15 and run upward.
In practice the split matters because ultra-high efficiency is usually specified where a single escaping particle can spoil a product or compromise safety. Semiconductor lithography, biological safety cabinets and aseptic pharmaceutical filling are the classic examples. If your application is closer to general critical filtration, a high efficiency class such as H13 HEPA filtration is usually the more cost-effective choice.
The Efficiency Classes That Matter, H13 to U16
Efficiency is quoted at a defined particle size, and the classes are not interchangeable. The table below sets out the ratings of the non-partition range.
| Class | Filtration Efficiency | Rated Particle Size | Standard |
|---|---|---|---|
| H13 | 99.97 % | 0.3 µm | EN 1822 |
| H14 | 99.995 % | 0.3 µm | EN 1822 |
| U15 | 99.9995 % | 0.12 µm | EN 1822 |
| U16 | 99.99995 % | 0.12 µm | EN 1822 |
Note the shift in rated particle size. HEPA classes are tested at 0.3 µm, while the ULPA classes are tested at the more penetrating 0.12 µm. A U15 rating is therefore a stricter claim than an H14 rating, even before the efficiency figure is considered.
Why Non-Partition Construction Lowers Operating Cost
Traditional high efficiency filters rely on aluminium foil or paper separators to hold the pleats apart. A non-partition filter replaces those separators with lines of hot melt adhesive, which frees up space that would otherwise be occupied by the divider.
The practical result is more usable media in the same face area. More media means lower face velocity and a design that reduces operating cost across the life of the filter — the core benefit of the non-partition approach. The structure is also more compact, which saves storage space before installation and allows a thinner profile where installation depth is limited. Where a facility still runs separator-based media, a high efficiency filter with partition remains available as a direct replacement.
Because replacement cost is only part of the picture, the case for non-partition media is usually made on total cost of ownership. A filter that runs at lower resistance draws less fan energy for every hour it is in service, and in a cleanroom that runs continuously the energy term quickly outweighs the purchase price. This is why the design brief for a new cleanroom tends to specify non-partition construction from the outset rather than treating it as a later upgrade.
How a Non-Partition ULPA Filter Is Built
Four elements define the construction of this range:
Anodized Aluminium Frame
The frame is an anodized aluminium profile, which keeps weight down and resists corrosion in the humid or chemically active air streams found in some production environments.
Ultra-Fine Glass Fiber Media
The filtration medium is ultra-fine glass fiber, the material that makes the U15 and U16 classes achievable at the rated particle sizes.
Hot Melt Adhesive Dividers
Hot melt adhesive lines hold the pleats apart in place of rigid separators, releasing space for additional media and simplifying the internal structure.
Polyurethane Sealant and Steel Mesh
Polyurethane seals the media to the frame to prevent bypass, while a painted steel mesh protects the upstream face of the filter during handling and installation.
Frame thickness is offered in 50 mm, 69 mm, 70 mm, 80 mm, 90 mm and 110 mm, and the maximum continuous operating temperature is 80 °C (180 °F).
Frame thickness also interacts with the mounting arrangement. Ceiling grid installations in cleanrooms normally use standard face sizes, while a bespoke housing may call for a specific depth to match an existing duct transition. Confirming both the face size and the depth before ordering avoids rework at installation.
Where ULPA Filtration Is Required
Ultra-high efficiency is specified where the consequence of particle escape is measured in product loss or safety rather than in comfort:
- Semiconductor fabrication, where lithography and wafer handling demand the lowest achievable particle counts.
- Biological safety cabinets and high-containment laboratories, where exhaust air must not carry viable particles.
- Aseptic pharmaceutical filling and sterile manufacturing, where contamination invalidates a batch.
- Cleanrooms operating at the highest cleanliness classifications, where terminal filtration sets the achievable class.
Because these rooms are also expected to run efficiently, ULPA stages are increasingly paired with modern low-energy air handling equipment; our review of trends in smart purification equipment for cleanrooms covers how control and monitoring are changing. Where filters are mounted in the ceiling grid, an EC fan filter unit provides the matched airflow source.
Choosing Frame Thickness and Size
Selection starts with the mounting arrangement and the load the filter must carry. A thicker frame provides more depth for media, which generally supports a lower resistance for a given airflow; a thinner frame suits installations where space is constrained. The range spans 50 mm to 110 mm for exactly this reason.
The number of filters needed follows from airflow rather than from guesswork. Divide the total supply airflow by the airflow a single filter can carry at the intended face velocity, then round up so that the ceiling grid is filled in whole panels. Sizing on face velocity rather than filter count alone keeps resistance within the design range and avoids over-running the media.
Where the application is critical but does not require the ULPA classes, the equivalent non-partition high efficiency filter offers the same construction in HEPA grades, which is often the more economical specification.
Installation, Testing and Replacement
A high efficiency filter only performs to its rating if it is installed and maintained correctly. The routine that matters most:
- Confirm the filter and gasket seal against the frame, with no visible gaps around the perimeter.
- Carry out an integrity scan after installation to verify that the media and seals are intact.
- Monitor pressure drop and replace on condition, rather than on a fixed calendar interval.
- Protect the upstream face during handling, and never install a filter with a damaged protection mesh.
- Match any replacement to the original class and frame thickness so the room classification is preserved.
Terminal filters do not work alone, however efficient they are; the upstream stages decide how long they last, as explained in our guide to multi-stage filters in HVAC systems.
Need Help Selecting a ULPA Filter?
RZJ manufactures non-partition high efficiency and ultra-high efficiency filters from H13 through U16, in a full range of frame thicknesses. Send us your required class, face size and airflow, and our engineers will confirm the right specification.
Contact Our Technical Experts for a Free Consultation